1. Field of the Invention
The invention relates to an internal combustion engine controller and a method of controlling an internal combustion engine, and in particular to a controller for and a method of controlling an internal combustion engine equipped with a cylinder pressure sensor.
2. Description of the Related Art
The sensitivity of a cylinder pressure sensor varies with time and there are individual differences in sensitivity between the cylinder pressure sensors. Thus, Japanese Patent Application Publication No. 2005-351146 (JP-A-2005-351146), for example, discloses an internal combustion engine controller that makes it possible to estimate the sensitivity of the cylinder pressure sensor. More specifically, in this controller, an estimate of the sensitivity of the cylinder pressure sensor is calculated based on the cylinder pressure at a predetermined crank angle θ0 in an intake stroke, the intake air pressure at the point, at which the crank angle becomes θ0+λ, and the cylinder pressure and the cylinder volume at at least two points of crank angles θ1, θ2 in a compression stroke. By using the accurate estimate of the sensitivity calculated in this way, it is possible to accurately obtain the information on the internal conditions of a cylinder and it is therefore possible to effectively use the information in controlling the internal combustion engine.
The cylinder pressure sensor is installed so as to be exposed to the inside of a cylinder of the internal combustion engine. Thus, when the sensor is exposed to a high-temperature gas, there is a fear that a thermal strain occurs in constituent parts and an error is caused in the output from the sensor. As measures against such an error, Japanese Patent Application Publication No. 6-265430 (JP-A-6-265430) describes a device for improving the accuracy in measuring pressure in terms of the hardware of the sensor.
However, when it is tried to improve the pressure measurement accuracy in terms of the hardware of the sensor as in the case of the above-described conventional cylinder pressure sensor, the construction of the sensor becomes complicated, which reduces practicality. Thus, it has been desired to eliminate the errors in the output caused by the thermal strain of the cylinder pressure sensor on the computer board side.